The history of how we heat our buildings, told by someone who has spent thirty years inside them.

 Five times in about a million years, people changed how they heat a room. Jaeson Cardiff has spent thirty years inside the rooms where that history still runs, first in the trade and then as an inventor working on carbon capture for commercial heating. Here he walks through all five changes: from a kept fire to the heat pump, by way of Roman floors, Korean ondol, a 1923 boiler with flowers cast into its face, and a basement experiment that put hydrogen next to a live furnace.